Narrative:
Grey Towers Castle was the first grandly-scaled house designed by noted Philadelphia architect Horace Trumbauer. Built for industrialist William Welsh Harrison in 1893, it was the source of many of Trumbauer's subsequent commissions to build homes for the early 20th century's industrial and commercial elite. It was said to be the third largest house in the country at the time of its completion. The building is sited on a hill above a sweeping lawn, now used for playing fields and for Commencement, and is approached by a road with an oak tree arcade. The exterior is modeled on a Northumbrian castle, featuring numerous large and small turrets and chimneys, crenellations, and machicolations, as well as an outstanding collection of gargoyles and grotesques. The interior grand rooms derive from several French Renaissance chateaus. While much of the interior furnishing is gone, the internal décor is largely intact, with intricate, often iconic mahogany carvings and paneling, cairn stone mantelpieces, ornate gold leaf light fixtures, beveled Belgian glass, and a large, intact, in-situ collection of American-made Baumgarten tapestry. Unlike many campus mansions called "the castle," Grey Towers is more purely a stereotypical castle in design. Compared to many great houses of its vintage, it is in relatively good condition, having been occupied and maintained by only two owners in its over 100 years of its existence.

As a lavish home for a scion of an industrial family, it is a living example of a time and social class largely vanished. It is widely recognized as one of the outstanding cases of American castle building. Of equal significance to the country's history is the nature of the fortune from which the Castle was built. Harrison and his two brothers had inherited a large sugar refinery. Sugar was among the first commodities of the global economy, and its role in the fate of many Africans brought to the New World is well documented. Moreover, the Harrison sugar business was bought out by a major sugar conglomerate, a late 19th-century instance of mergers and acquisitions.

Gray Towers Castle has also influenced the architecture of other portions of Arcadia's campus. Buildings of the 1960s repeated the stone cladding of the historic structures; and while others introduced new exterior surfaces, they maintained the flat roof of the castle and, in the 1990s, introduced round features echoing the castle's turrets.